All interesting ideas here, most on the acidic side of the spectrum. May I suggest an alkaline solution?
I have been throwing my fireplace wood ash on my gravel driveway for the past months, maybe a quart a day or so on 200 sqft. It's just a trial. Of course the large chunks of ash will stay on top of the gravel, but the fine ash should travel down to the soil where it should give it a good whack to the alkaline. I do keep it away from the acid-loving azaleas and berries obviously. At the moment it's to early to tell if it's effective but I would be very surprised if it's not. Of course you do get these black ash spots but hey I couldn't care less what the neighbors think. Just don't walk it into the house (yuck).
Another solution is just to create shade for your area - duh!
And flameweeding is something I also find very effective. Here in The Netherlands I flameweed a different driveway (200ft long) gravel driveway in 2 hours. I do this every other week (don't let the weeds grow to big!) so that's about one hour per week, but it's a 2500 sq ft area I'm talking about.
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